Modern Ship & Shipbuilding Terminology

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Bermuda Rig: A fore-and-aft rig in which the mainsail is triangular in shape; also sometimes referred to as a Marconi rig. A Bermuda rig also includes one headsail.

Center of Effort: Theoretical center or focus of wind force on a single sail or the theoretical center of the sum of wind forces on multiple sails.

Conning Tower: A raised and armored observation post on a warship or submarine. On a submarine the conning tower often acted as an entrance to the submarine and as a compartment from which the periscopes were used to direct the boat and launch torpedo attacks.

Deadweight: Deadweight tonnage or DwT is the absolute maximum weight that a ship can safely carry when fully loaded. It includes crew, passengers, cargo, fuel, water, and stores. Often expressed in long tons or metric tons. Acronym: dwt. It is measured by measuring the displacement difference when the vessel is empty (or light) and fully loaded.

GRT: Gross Register Tonnage is the cubic capacity of all enclosed spaces of a ship, more often used then NRT for calculating cargo capacity of a vessel. A Gross Register Ton is equal to 2.83 cubic meters or 100 cubic feet.

Gusset: A metal or wood brace reinforcing a joint where two or more structural parts meet, such as hull frame members.

Headsail: Any sail set forward of the foremost mast of a sailing vessel.

In Ordinary: When a commissioned naval vessel is placed in ordinary, it is 'mothballed' or stored for later use, later re-assignment or possibly final decommissioning.

Lightship: An anchored ship acting as a floating lighthouse where building a lighthouse was not possible or impractical. Lightships would display a light at the top of a mast and in case of fog would sound a fog signal.

Metacenter: The point of intersection (M) of the vertical line through the Center of Buoyancy (B - centroid of the displaced volume of water) and the centreline of the hull. To ensure that a ship will come upright when she is heeled (listing) the Metacentre must be above the Centre of Gravity (G) of the hull.

The more distance between the Metacenter and Center of Gravity, also called the Metaheight, the more 'stable' the hull.

Moon Pool: The opening in the hull of an offshore drilling vessel through which drilling equipment passes.

RAS:Replenishment at sea. Term for a Navy ship being re-supplied with fuel and other stores by a supply-ship while at sea.

Tender: A vessel attending to another vessel, in particular one that ferries supplies and personnel between ship and shore.

Trimaran: A fast sailboat with three hulls, normally having a larger main center hull and two smaller outrigger hulls called amas, one on either side, connected to the center hull by a framework of struts called akas. The words aka and ama originate from the original 'outrigged' East Indies Caracore or Proa.